The present invention relates to a horizontal deflection circuit used in a display unit provided with a CRT.
In general, a resonant circuit in a horizontal deflection output portion of a conventional display unit includes a single tuned resonant circuit composed of a horizontal deflection coil and a resonant capacitor. In the resonant circuit, a retrace period (flyback period) T.sub.ret is shown as the half of a resonant period, that is ##EQU1## where L.sub.1 represents the inductance of the horizontal deflection coil and C.sub.1 represents the capacitance of the resonant capacitor. Further, when a deflection current at the time of scanning the right end of a screen is represented by i.sub.1 and the peak value of a flyback pulse voltage generated between both ends of the deflection coil during the retract period is represented by V.sub.op, the following relation is established. ##EQU2##
Here attention is directed to the figure of merit (FM) as defined by the following equation (2). ##EQU3##
The numerator in the equation (2) shows the change of total magnetic flux required for shifting the electron beam of the CRT from the right end of the screen to the left end of the same. The denominator in the equation (2) shows the product of the pulse voltage and the retrace period.
If the waveform of the flyback pulse is a perfectly square waveform, the value of the equation (2) must be equal to 1. However, in fact, the waveform of the flyback pulse is a waveform having half a cycle of a sine curve. Accordingly, as shown in the equation (3), it is quite natural that the value of the equation becomes smaller than 1 (that is, 0.64).
When the figure of merit (FM) is small, it is necessary that the peak voltage of the flyback pulse is increased to attain the same quantity of total flux change. However, expensive parts having characteristics such as durability against high voltage must be used for the horizontal output transistor, the damper diode and other parts of the horizontal deflection circuit for the purpose of increasing the peak voltage of the flyback pulse. If parts inferior in the characteristic thereof is used, the circuit thus constituted by the parts has so little play in it that stable horizontal deflection cannot be carried out as factors such as temperature are changed. If it is possible to bring the figure of merit (FM) closer to the ideal value 1 (one), parts not having such characteristics can be used for the horizontal deflection circuit for performing stable horizontal deflection with satisfactory retrace capacity. The circuit constituted by such inexpensive parts can be employed widely for various CRTs.